61:8 Dr. F. E. Beddard on the Blow-holes and 



this lack of connection between the rostrum throughout its 

 length with the nasal cartilages persists into the adult state 

 (or practically so), since Messrs. Pouchet and Beauregard 

 figure no connection between the two so far back as a 

 distance of 40 cm. from the snout in a head of a "young 

 male/' which is itelf (the head) 1-30 M. long *. The con- 

 nection of the two would appear, therefore, to be quite 

 secondary, and there are other facts which support this view. 

 These concern the development of the cartilages in question. 

 The rod-like rostral cartilage seems to be growing from 

 before backwards, and the growth seems to be taking place 

 in the formed cartilage and not in the surrounding tissues 

 of the head. It is quite otherwise with the cartilages of the 

 nasal tubes. 



Here the first beginnings of the nasal cartilages are seen 

 to be — as is, of course, well known in the development of 

 cartilage — a condensation of the nuclei of the mesoblast in 

 the neighbourhood of the nasal grooves. 



The actual condensation of the tissue to form the '"' pro- 

 cartilage " begins very early in the head, immediately 

 behind the anterior groove into which the two nasal tubes 

 open. Actual cartilage is not formed until later, about 

 •75 mm. behind the said groove. The first cartilage to be 

 formed is that which lies on the dorsal surface of the right 

 nasal cavity ; a very short way further back the median 

 internasal cartilage puts in an appearance, and a little later 

 still that of the left nostril. These cartilages are every- 

 where independent from each other as cartilages in the 

 present region of the snout ; but they are all connected by 

 the dense tissue with crowded nuclei which is the forerunner 

 of the cartilage. It will be noted, therefore, that the 

 asymmetry of the blow-holes is seen also in their cartilages. 

 I could find no trace whatever here, or in the liinder region 

 of the nasal cartilages, of any extension on to the ventral 

 surface of the nasal tube, such as is represented by Kiikenthal 

 to occur in PhoccB7ia f. They are here purely dorsal. Early 

 in the series of sections the cartilage of the right nostril 

 extends more or less right along it. But as we pass back- 

 wards in the series this transversely elongated cartihige 

 becomes divided into two, of which the outermost extends 

 back for a very short way and then ends. The other 

 reaches much further towards the skull. 



* Loc. cit. pi. vi. fig. 2. 



t ''Die Walthiere/' Denksclir. Nat.-Med. Ges. Jena, Ed. iii. Tlieil 2, 

 p. 322 &c., pi. xxjii. figs. 4, 5, 6. 



